NUMERICAL MODELING OF THE SPATIAL PROFILES OF HIGH-ORDER HARMONICS

The far-field spatial distributions of high-order harmonics in an ioni zed medium have been investigated using a computer model that includes both the single atom effects and the collective effects of the medium . The results show that depletion of the non-linear medium due to ioni zation and radial phase variations across the gas jet cause broadening and complicated structures in the far-field spatial distributions. Th ese phase variations are due to three factors: focusing, ionization, i .e. depletion of the non-linear medium and electron dispersion, and in tensity-dependent phase variations of the atomic dipoles.